The present application pertains to a method for making amorphous semi-conductor layer and particularly (but not exclusively) layers of the type described as alpha-Si:H layer configuration commonly called an amorphous, hydrogen doped, silicon layer. Microelectronics developed rapidly with the advent of semiconductor components. The development of semiconductors has already a long history behind it, and presently the so called amorphous alpha-Si:H layers are of increasing importance. The reason is that single crystal Si wafers are still relatively expensive and a more economical way of making them is presently not envisioned. For this reason it is of great interest to replace the single crystals by amorphous layers; the same can be said with regard to other semiconductors and here for example so called alpha-Ge:H layers or alpha-B:H configurations, also amorphous carbon is of interest as well as intermetallic compounds.
Generally speaking the following methods are known and have been practiced for making semiconductor layers such as vapor depositing; cathode sputtering; formation of an epitaxy layer by a molecular beam; thermal decomposition of gaseous compounds of the particular semiconductor followed by precipitation on a previously prepared substrate in a reaction chamber (CVD or photo CVD); decomposition by means of glow discharge. These methods will be critically evaluated next.
The vapor depositing method is suitable for the manufacture of pure alpha-semiconductor layer on account of the ensuing separation. A desired hydrogen-doped layer configuration when produced through the reactive sputtering, using an H.sub.2 carrier gas blend have been found generally to produce rather inferior products as far as electronic properties are concerned. Better qualities result from employing molecular beam epitaxy methods but in the near future an industrial application is still not within the realm of practical application, even if the method is basically modified in different ways. The reason being that the precipitation rates are extremely slow and one simply does not know at this point how to increase these rates to a more economical level. In addition, one needs a very powerful differential vacuum pumping system since the final pressure of 1/10.sup.8 torr has to be produced.
The thermal decomposition and glow discharge methods using appropriate temperature controlled substrates do provide the desired layers without requiring any further modification and subsequent treatment but the precipitation rate of only about 1 micrometer/hour is rather slow. Moreover, the precipitation of these layers is uncontrolled everywhere in the reaction chamber. Adhesion of the precipitated layer on the heated substrate is not very good in parts and therefore not suitable for making from them thin layer transistors.
Chemical vapor depositing generally is a gas precipitation initiated through a purely thermal process. A photochemical vapor depositing implies dissociation either through infrared laser energization e.g. under utilization of a CO.sub.2 laser or through electronic laser stimulation for example by a so called Excimer-Laser.
A representative state of the art includes U.S. Pat. No. 4,521,447 and German printed patent application 2,807,803.